Cystitis/Bladder infections

Contains_Mild_Peril

I've had this problem myself, so I can sympathise. The main thing is to drink LOTS of water. Cystitis is often caused by infection, but can also be caused by other factors like dehydration, or irritants such as toiletries. You should wash regularly with plain water, no soap etc.
Whatever the cause, drinking huge quantities of water (not caffeinated, alcoholic or sugary drinks) at the first sign of trouble should help alleviate it.
Tampon withdrawal cords can transfer bacteria from the anal area to the urethra, so it's probably best to use pads instead, which should, of course, be changed very frequently.
You may find Angela Kilmartin's self-help books on cystitis to be helpful. I know I did.

Dormouse

I know this is not a solution to OP's immediate problem, but just thought I'd mention that there might be something hormonal going on (like one of the previous posters said). I used to get cystitis all the time, until I had a baby, and have not had a single attack since (been 3 years now!). Really don't know exactly what the connection is, but it's amazing.

So there is hope that you might not have to put up with it forever, as some hormonal thing might make a difference at some point.